The purpose of this project is to develop an animal model to evaluate cardiac valves in vivo. This animal model system is utilized in a multidisciplinary manner, including the fields of surgery, physiology, pathology, engineering and technology development. We have shown that bioprosthetic values implanted in juvenile sheep demonstrate the same pathologic alterations of degeneration and calcification as those implanted in humans; however, the development of these alterations is accelerated in sheep as compared to humans. Nearly 600 porcine aortic or bovine pericardial bioprosthetic valves from fourteen sources and of more than thirty different types have been implanted in the animal model system to: 1) assess the characteristics of the pathologic changes, 2) compare the alterations in different types of valves, 3) compare the alterations in different types of valves; 4) compare the alterations occurring in valves implanted in the mitral versus the tricuspid positions, and 4) evaluate valves treated prior to implantation with processes to retard or to eliminate the calcification and degeneration processes. Due to these types of observations, clinical trials have been initiated with two new types of bioprosthetic valves. Equally important, if not more so, at least seven types of valves have been rejected from consideration for clinical use. Both the positive and negative results of studies of these processes have added insight to the mechanisms of calcification, degeneration and malfunction of prosthetic cardiac valves. Additionally, the model is being utilized to validate ultrasonic techniques, including color- encoded, two-dimensional Doppler, for the characterization of bioprosthetic, mechanical, and synthetic leaflet valve velocity flow turbulence profiles and for the noninvasive detection of valve failure.